This disclosure relates to polycarbonate compositions, and in particular to articles comprising polysiloxane-polycarbonate compositions.
Thermoplastic compositions comprising polycarbonates are known for their impact strength, transparency, and melt-flow characteristics, and are used in the manufacture of articles and components for a wide range of applications, from automotive parts, to packaging materials, to electronic appliances. The properties of thermoplastic polycarbonate polymers may be further adjusted by the inclusion of discrete, compositionally different polymer units. Condensation copolymers comprising polyesters and polycarbonates, and particularly those compositions additionally comprising polysiloxanes, exhibit better low temperature ductility and thick section impact than corresponding non-polysiloxane-containing polyester polycarbonates.
However, copolymer combinations containing aromatic ester units, carbonate units, and siloxane units have been found to exhibit phase separation, as evidenced by low transparency and high degrees of haze. These optical characteristics can limit the utility and potential applications of such copolymers. There accordingly remains a need for copolymers containing aromatic ester units, carbonate units, and siloxane units wherein the melt flow and/or ductility properties of the combination is achieved while maintaining high transparency and low haze.
The ASTM D1003-00 haze measurement on a flat molded bar (typically ⅛ inch thickness) however, does not fully characterize the observed haze on the polycarbonate (PC) siloxane molded parts. Even for PC Siloxane samples which approach standard PC homopolymer in appearance when viewed through the flat surface of the part and when measured by standard ASTM D1003 method (that is 1% or lower haze), the edges of the samples show a very high level of visible haze as compared to PC homopolymer. This edge haze, which appears to be a result of dispersion of light by the siloxane domains as it passes through the part, is aesthetically unacceptable in many types of complex design molded parts, where these hazy edges are often visible through the otherwise clear part surfaces.
There accordingly remains a need in the art for PC siloxane molded parts with low edge haze.